Spectrophotometry is the study of electromagnetic waves in the visible, near-ultraviolet, and near-infrared spectra. A spectrophotometer is a light measuring device that is configured to measure various characteristics of light, including intensity, color, and/or wavelength. Spectrophotometers have a wide range of uses. For instance, they may be used to detect colors on display devices such as televisions, projectors, monitors, and camcorder viewfinders. Alternatively, spectrophotometers may be used in printing devices to calibrate the colors printed.
Typically, when used as a color detector, the spectrophotometer may include a light source, a light-to-electrical transducer, known as a photodetector, and a filter. In one instance, the light is projected toward an object. The object reflects the light, and the photodetector receives the reflected light. The light may pass through the filter before being received by the photodetector so that the color may be detected. Specifically, the filter is configured to only allow light having a specific range of wavelengths to pass through. This is known as filter response. Light that passes through the filter causes the photodetector to generate an electrical signal. The magnitude of this electrical signal indicates the amount of the specific color of light present. An array of photodetectors and filters allow for the spectrophotometer to receive more detailed information. For example, an array of photodetectors each having a filter tuned to filter light at different wavelengths would be able to detect finer resolution on the input light spectrum than a smaller number of filters would.
While useful in many technology areas, spectrophotometers have several problems, especially related to the transmission characteristics of the filter. For instance, in addition to only allowing different colors to pass through them, filters tuned to allow the transmission of light at different frequencies may also allow the transmission of different amounts of light. In other words, the magnitude of light that passes through one filter may be greater than the magnitude of light that passes through another filter. If this difference is a result of the filter configurations, then it may lead to inaccurate color determinations by the color detector if not corrected for. In addition, some filters may exhibit a lower signal-to-noise ratio than other filters due to low input signal strength in that filter bandwidth or the inability of any one filter by its design to allow for a high enough transmission within the band of interest. In this context, “noise” may be light interference from colors outside the filter's tuned spectrum of wavelengths or electrical noise in the photodetector. Attempts to amplify the transmission by the filter may also result in amplifying the noise. Again, this may also lead to inaccurate color determinations by the color detector. Photodetectors may have a different response to a given amount of light power depending on the particular wavelength, i.e. color, of the light that reaches the photodetector. For example, a “red” light could generate an electrical signal that is ten times greater than generated by a “blue” light of equivalent light power. Photodetectors can only detect a limited range of useable light. Light sources may generate a different amount of light as a function of wavelength.
Accordingly, a spectrophotometer or color detector is needed that equalizes the combined light source, filter, and photodetector responses to provide more accurate color determinations by the color detector.